Television display apparatus provided with a circuit arrangement for generating a sawtooth deflection current

ABSTRACT

Television display apparatus including a circuit arranged for combined line deflection and supply voltage stabilisation, comprising a transformer. The transformation ratio can be freely chosen because the path between the deflection and stabilizing section is blocked in the retrace time.

United States Patent 1 [111 3,912,971

Houkes Oct. 14, 1975 TELEVISION DISPLAY APPARATUS PROVIDED WITH ACIRCUIT ARRANGEMENT FOR GENERATING A SAWTOOTH DEFLECTION CURRENTInventor: Henk Houkes, Nijmegen,

Netherlands Assignee: U.S. Philips Corporation, New

York, NY.

Filed: Feb. 19, 1974 Appl. No.: 443,863

Foreign Application Priority Data Mar. 8, 1973 Netherlands 7303252 US.Cl 315/408; 315/387 Int. Cl. HOlJ 29/70 Field of Search 3l5/387, 399,408, 409,

SYNC

V. OSC.

OUTPUT [56] References Cited UNITED STATES PATENTS 3,401,306 9/1968Bolvin et a1 315/408 X 3,441,791 4/1969 Beck 315/408 3,449,623 6/1969Dietz 315/408 3,512,040 5/1970 Lester 315/408 X Primary ExaminerT. H.Tubbesing Attorney, Agent, or FirmFrank R. Trifari; Henry I. Steckler 8Claims, 5 Drawing Figures Patent Oct. 14, 1975 Sheet 1 of3 3,912,971

SYNC SEF! V. 080. V. OUTPUT US. Patent Oct. 14, 1975 Sheet 2 of 33,912,971

TELEVISION DISPLAY APPARATUS PROVIDED WITH A CIRCUIT ARRANGEMENT FORGENERATING A SAWTOOTH DEFLECTION CURRENT The invention relates totelevision display apparatus provided with a circuit arrangement forgenerating a sawtooth deflection current through a line deflection coil,said coil being a part of a network furthermore comprising at least atrace capacitor a retrace capacitor and a first diode through which thedeflection current flows during part of the trace time while saidcurrent flows through a second diode and a controllable switch duringthe other part of the trace time, a primary winding of a transformerbeing incorporated between a direct voltage source and the switch and asecondary winding being connected through a third diode to the network.

Such a circuit arrangement is described in German patent application No.2,130,902 and is the combination of a line deflection circuit and aswitched supply voltage stabilisation circuit in which a single element,the above-mentioned switch, serves for fulfilling the two saidfunctions.

In this German patent application no requirement has been imposed on thetransformation ratio of the transformer, i.e., the ratio between thenumber of turns on the secondary winding and the number of turns on theprimary winding. In practice, however, this ratio is determined in thefirst place by the ratio between the nominal value of the supply voltagesupplied by the direct voltage source and the desired value of the tracevoltage, i.e., the voltage to which the deflection coil is connectedduring the trace time. The value of the trace voltage is in turndetermined by the desired intensity of the deflection current andconsequently by the value of the impedance of the deflection coil. Inthe second place the said transformation ratio also depends on the ratiobetween the conduction period of the switch and the iine period, whichratio itself is a function of the maximum fluctuation to be expected ofthe supply voltage generally derived from the electrical mains. It hasbeen found in the known circuit arrangement that not everytransformation ratio is possible because a distortion of the deflectioncurrent under given circumstances may occur. An object of the inventionis to improve the said circuit arrangement in this respect and to thisend the circuit arrangement according to the invention is characterizedin that it includes switching means for blocking any current in thesecond diode in the retrace time.

As a result of the step according to the invention any arbitrarytransformation ratio may be chosen as desired so that a greater degreeof freedom is achieved in the design of the circuit arrangement.

The invention will be described in greater detail by way of example withreference to the Figures shown in the drawing.

FIG. 1 shows a first embodiment of television display apparatusaccording to the invention,

FIG. 2 shows some waveforms to explain the operation of the embodimentof FIG. 1,-

FIGS. 3 and 4 show different embodiments of circuit arrangements intelevision display apparatus according to the'invention and FIG. 5 showssome waveforms to explain the operation of the embodiment of FIG. 4.

The television display apparatus of FIG. I has a high frequency tuner Ifor connection to an aerial 2, an intermediate frequency amplifier 3, adetector 4 and a video amplifier with a colour decoder 5 applying thecolour signals to a colour television display tube 6. This tube has anacceleration anode 7 and is provided with a coil Ly for the horizontal(line frequency) deflection and a coil L, for the vertical (fieldfrequency) deflection.

Line synchronizing pulses which are applied to a line oscillator 9 areseparated from the output signal of detector 4 by means of synchronizingseparator 8, as well as field synchronizing pulses which are applied toa field oscillator 10. Oscillator 10 controls a field output stage 11which supplies the deflection current for coil L y. Line oscillator 9controls a driver stage D, which supplies switching pulses for acontrolled switch, for example, a switching transistor T, of a linedeflection output circuit to be described hereinafter.

A trace capacitor C, is arranged in series with line deflection coil Lyand a diode D with the given conductivity direction and a retracecapacitor C, are arranged in parallel with the series arrangement thusformed. Capacitor C, may alternatively be connected in parallel acrosscoil Ly. The said four elements only show the principle circuit diagramwith the main components of the deflection section. This section may beprovided, for example, in known manner with one or more transformers formutual coupling of the elements, with devices for centering andlinearity correction and the like.

A secondary winding L of a transformer T is arranged in series with adiode D whose cathode is connected to the junction of elements D,, C,and Ly and to the anode of a diode D The cathode of diode D is connectedto the collector of a transistor Tr of the npn type whose emitter isconnected to one end of a primary winding L of transformer T and to thecollector of a transistor Tr of the npn type. The positive terminal of adirect voltage source B is connected to the other end of winding L, andthe negative terminal is connected to the emitter of transistor Tr. Thisnegative terminal is also connected to the free ends of elements L D,,C, and C, and may be connected to ground of the circuit arrangement.

One end of a further secondary winding L of transformer T is directlyconnected to the emitter of transistor Tr and the other end thereof isconnected through a resistor R,, to its base. Other secondary windingsare wound on the core of transformer T across which there are voltagesserving as supply voltages for other parts of the television displayapparatus. One of these windings, winding L is shown in FIG. 1 andgenerates the EHT for the acceleration anode 7 of tube 6 with the aid ofan EHT rectifier D across a smoothing capacitance C,. The winding senseof the windings of transformer T shown is denoted by polarity dots inthe Figure.

During a first part of the line trace time diode D conducts. The voltageacross capacitor C, is applied to deflection coil L through which asawtooth deflection current flows. At a given instant transistor Trbecomes conducting. When approximately in the middle of the trace timethe deflection current reverses its direction,

diode D is blocked and both transistor Tr and diode D become conductingso that the deflection current then flows through transistor Tr whilediode D is blocked. At the end'of the trace time transistor Tr is cutoff. An oscillation, the flyback pulse, is produced across capacitor C,-while the energy stored in winding L and derived from source B producesa current through diode D When the voltage across capacitor C, hasbecome zero, diode D becomes conducting: this is the beginning of a newtrace time. Diode D remains conducting until transistor Tr is renderedconducting while the energy in winding L is transferred to winding LStabilisation is provided for example by the voltage across capacitor C,being fed back to driver circuit Dr in which a comparison stage and amodulator ensure that the conductivity time of transistor Tr is variedin such a manner that the said voltage and consequently the amplitude ofthe deflection current remain constant.

In FIG. 2a the voltage v across capacitor C,, and in FIG. 2b the voltageat the junction of winding L and diode D and in FIG. the voltage at thecollector of transistor Tr is plotted as a function of time. The symbolT indicates the line period, while t, denotes the retrace time and 5 Tdenotes the part of period T when transistor Tr conducts. During thetime when diode D conducts the voltage in FIG. 2b is equal to that ofFIG. 2a, i.e., the flyback pulse with amplitude V during the time t andzero in the part of the trace time when transistor Tr does not conduct.At the instant when transistor Tr is rendered conducting its collectorvoltage becomes substantially zero. The voltage V from source B is thenpresent across winding L If the transformation ratio of windings L and Li.e., the ratio between the number of turns on winding L and those onwinding L is equal to l:n, the voltage of FIG. 2b is equal to nV duringthe time interval 8 T The collector voltage of transistor Tr is equal tothe voltage in FIG. 2a

during the time interval 1,- divided by the ratio n and supplemented byvoltage V It has been assumed in the foregoing that transistor Trconducts during the time interval 8 T which will be describedhereinafter.

When V is the direct voltage across capacitor C, if this capacitor has asufficiently high capacitance, or when it is the direct voltagecomponent of the voltage across this capacitor if it has a comparativelylow capacitance in view of the so-called S-correction, V is equal to themean value of the voltage v. In fact, no direct voltage component can bepresent across coil Ly. There applies that T 0/ win The means value ofthe voltage across winding L is also zero so that there applies thattime interval t the base voltage is negative relative to the emittervoltage. Consequently transistor Tr does not conduct during the timeinterval r,. The diode D incorporated between the base and the emitterensures that the base emitter voltage cannot become more negative thanis admitted. This diode may alternatively be arranged in series with theresistor R,, as is the case in FIG. 1. During the first part of thetrace time in FIG. 2b the transistor Tr does not conduct. It doesconduct during the time interval 5 T provided that the transformationratio between windings L and L and resistor R have suitable values.

The above-described operation of transistor Tr is necessary for thefollowing reason. During the retrace time its collector voltage is equalto v while the emitter voltage is equal to In the middle of time t,-these voltages are equal to V and to Dependent on the value of theflyback ratio V and V are proportional, i.e., V a: V in which the number8 10 ifz 1/6. The above-mentioned condition then is:

Filling this in in formula (3) results in:

that is l n l+ as Without the step according to the invention transistorTr would conduct during the retrace time if the ratio n satisfiesformula (4), that is to say, the path between the deflection andstabilizing section of the circuit arrangement would not be blocked.Since diode D conducts during the same time, windings L and L would beshort-circuited by transistor Tr and diodes D and D so that the flybackpulse across capacitor C, would be cut off and the deflection currentwould be distorted.

A transformation ratio of more than 1 may be necessary if deflectioncoil L has a comparatively high impedance. The current which is thenrequired may only be supplied by a higher V for a given V whichaccording to formula (3) is only possible by a higher n. It mayalternatively occur that voltage V,, is comparatively low which leads tothe same step. Itmay be noted that the maximum collector voltage oftransistor Tr is equal to V 01V T4- V,,= V =(I +cr8) 1 after filling informula (3) and is therefore independent of ratio n, while the maximumcollector current, i.e., the sum of the deflection current and thecurrent through winding L, at the end of the trace time can be made aslow as possible by a suitable design of the circuit arrangement.

As is known a capacitor C may be arranged between windings L and L whichcapacitor has for its object to prevent parasitic oscillations which maybe caused by the leakage inductance existing between the said windings.In order that no line frequency voltage is present across capacitor C itmay be arranged between taps of windings L and/or L when ratio n is notequal to 1. For n I capacitor C is arranged between the collector oftransistor Tr and a tap on winding L with which the transformation ratiobetween winding L and the upper part of winding L is equal to 1:1.Source V may be connected to taps on winding L for example, when usingtelevision display apparatus according to the invention in countrieswhere different mains voltages are used.

In the embodiment of FIG. 3 in which for the sake of simplicity only theimportant elements are shown transistor Tr is absent. If transformationratio n satisfies condition (4), diode D is prevented from carrying acurrent during the retrace time by incorporating a diode D in serieswith winding L It is true that diode D is almost brought to theconducting state so that the flyback pulse is also present at thecollector of transistor Tr, but a current cannot flow through diode DDiode D is shunted by a resistor R which ensures that the parasiticcapacitance relative to ground of the collector of transistor Tr andelements connected thereto is already discharged at the instant whentransistor Tr is rendered conducting. This resistor may alternatively bearranged between the collector of transistor Tr and one of the terminalsof source B, but the dissipation therein would be greater. Theresistance of resistor R is high enough in order for the current flowingtherethrough and through diode D to be negligibly small. It will,however, be evident that the separating action of transistor Tr in FIG.1 is better. It will be noted that it is more advantageous to arrangediode D between winding L and transistor Tr than to arrange it betweenwinding L and source B. In the latter case there is no point on windingL connected to point of fixed potential and capacitor C cannot beprovided.

It will be noted that the maximum collector voltage of transistor Tr isequal to voltage V if the ratio 11 is larger than the above-mentionedlimit value and is therefore directly proportional to ratio 11. On theother hand the maximum collector current is inversely proportional toratio 11 when the current through winding L is not taken into account sothat the switching capacity of transistor Tr, i.e., the product of thecollector peak voltage by the collector peak current, is independent ofn. When ratio n is lower than the limit value given by formula (4) theswitching capacity is higher because the collector peak voltage of thetransistor is higher than voltage V. Due to the step according to theinvention the optimum switching capacity can thus be utilized.

FIG. 4 shows an embodiment of the circuit arrange ment according to theinvention in which the cathode of diode D is not connected to capacitorC, but to capacitor C,. Such a modification is also described in thesaid German patent application.

During the conductivity time of diode D that is, dur ing the retracetime and the first part of the trace time the voltage V across capacitorC, is also across winding L see FIG. 5a in which the capacitance ofcapacitor C, is assumed to be very large. Since the voltage acrosswinding L is equal to (V /n), the collector voltage of transistor Tr isequal to (see FIG. 512). During the conductivity interval 6T oftransistor Tr the voltage V is present across winding L so that thevoltage nV is present across winding L In a manner corresponding to thatin FIG. 1 we can write V (1 5)T nV 8 T which is:

Without the step according to the invention diode D would conduct duringthe retrace time if the peak value V of the voltage across capacitor C,were higher than or equal to The condition therefor is:

This is filled in in formula (3) and we have:

With a and 8 z /2 a limit value of approximately 0.2 is obtained. Sincethe maximum value of 8 is equal to l z, the minimum limit value isapproximately equal to 1.2/04). A low value of n will be chosen ifdeflection coil L has a comparatively low impedance and/or if theavailable voltage V,, is comparatively high. The maximum collectorvoltage of transistor Tr is equal t0 and is therefore independent ofratio n.

A series network R C which damps parasitic oscillations which mightoccur when the ratio n is much lower than 1 is connected in parallelwith winding L As is the case in FIG. 3 an embodiment according to FIG.4 may be considered in which transistor Tr is absent while the parallelarrangement of diode D and resistor R is arranged in series with windingL In such an embodiment the switching capacity of transistor Tr is alsoindependent of n.

What is claimed is:

1. Television display apparatus provided with a circuit arrangement forgenerating a sawtooth deflection current through a line deflection coil,said coil being a part of a network furthermore comprising at least atrace capacitor, a retrace capacitor and a first diode through which thedeflection current flows during part of the trace time of the sawtoothcurrent while said current flows through a second diode and acontrollable switch during the other part of the trace time, a primarywhere a is the ratio between the retrace voltage and its direct voltagecomponent.

3. Television display apparatus as claimed in claim 1, in which thethird diode is connected to the trace capacitor, characterized in thatthe ratio between the number of turns on the secondary winding and thenumber of turns on the primary winding is at least equal toapproximately (1.2/069 /awhere a is the ratio between the retracevoltage and its direct voltage component.

4. Television display apparatus as claimed in claim 1, characterized inthat said switching means comprises a transistor arranged in series withthe second diode while the base of said transistor receives a blockingvoltage in the retrace time.

5. Television display apparatus as claimed in claim 4, characterized inthat the control means of the transistor includes a further secondarywinding of the transformer.

6. Television display apparatus as claimed in claim 1 in which thesecond diode is connected to the controllable switch, characterized inthat a fourth diode is arranged in series with the primary winding.

7. Television display apparatus as claimed in claim 6, characterized inthat the fourth diode is shunted by a resistor.

8. A circuit arrangement for generating a sawtooth deflection currentthrough a line deflection coil powered from a direct voltage source,said circuit comprising a trace capacitor to couple to said coil, aretrace capacitor coupled to said trace capacitor and a first diodecoupled to said retrace capacitor through which the deflection currentflows during part of the trace time of the sawtooth current, a seconddiode coupled to said retrace capacitor, a controllable switch coupledto said trace capacitor, said current flowing through said contime.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,912,971 DATED October 14, 1975 INVENTORG) I Henk Houkes Itis'certifi ed that error appearsin the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Claim 3, col. 8, line 8, cancel "(1.2/069/OL" and insert Signed andSalad thus Twentieth Day Of July 1976 [SEAL] AUG-$1.

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uj'Paremsand Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OFCORRECTION PATENT NO. 3,912,971 DATED October 14, 1975 iN-VENTO I HenkHoukes It is certified that error appearsin the above-identified patentand that said LettersPatent are hereby corrected as shown below:

Claim 3, col. 8, line 8, cancel (1.2/069/or" and insert Signed andScaled thus Twentieth Day of July 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofParemsand Trademarks

1. Television display apparatus provided with a circuit arrangement for generating a sawtooth deflection current through a line deflection coil, said coil being a part of a network furthermore comprising at least a trace capacitor, a retrace capacitor and a first diode through which the deflection current flows during part of the trace time of the sawtooth current while said current flows through a second diode and a controllable switch during the other part of the trace time, a primary winding of a transformer being incorporated between a direct voltage source and the switch and its secondary winding being connected through a third diode to the network, characterized in that the circuit arrangement includes switching means for blocking any current in the second diode in the retrace time.
 2. Television display apparatus as claimed in claim 1 in which the third diode is connected to the retrace capacitor, characterized in that the ratio between the number of turns on the secondary winding and the number of turns on the primary winding is at least equal to approximately
 3. Television display apparatus as claimed in claim 1, in which the third diode is connected to the trace capacitor, characterized in that the ratio between the number of turns on the secondary winding and the number of turns on the primary winding is at least equal to approximately (1.2/069 / Alpha where Alpha is the ratio between the retrace voltage and its direct voltage component.
 4. Television display apparatus as claimed in claim 1, characterized in that said switching means comprises a transistor arranged in series with the second diode while the base of said transistor receives a blocking voltage in the retrace time.
 5. Television display apparatus as claimed in claim 4, characterized in that the control means of the transistor includes a further secondary winding of the transformer.
 6. Television display apparatus as claimed in claim 1 in which the second diode is connected to the controllable switch, characterized in that a fourth diode is arranged in series with the primary winding.
 7. Television display apparatus as claimed in claim 6, characterized in that the fourth diode is shunted by a resistor.
 8. A circuit arrangement for generating a sawtooth deflection current through a line deflection coil powered from a direct voltage source, said circuit comprising a trace capacitor to couple to said coil, a retrace capacitor coupled to said trace capacitor and a first diode coupled to said retrace capacitor through which the deflection current flows during part of the trace time of the sawtooth current, a second diode coupled to said retrace capacitor, a controllable switch coupled to said trace capacitor, said current flowing through said controllable switch and said second diode part of the trace time, a transformer having a primary winding to coupled to said direct voltage source and coupled to the switch, and a secondary winding, a third diode coupled to said secondary winding and one of said capacitors, and switching means coupled to said second diode for blocking any current in the second diode in the retrace time. 